1. Field of the Invention
The present invention relates to apparatus for effecting an interruption of any optional duration in the redialling operation of a redialling circuit having an interrupt loop which interrupts dialling for a finite duration, the circuit having more specifically a first supply terminal connected to a first potential of a value higher than a predetermined threshold value, a second supply terminal connected to a second potential which is negative relative to the first potential, an output terminal supplying during the said finite duration of the interruption and when an interrupt command is transmitted by a memory of the circuit an interrupt voltage which is also higher than the threshold value and an input terminal which efficiently interrupts the redialling operation when the said interrupt voltage is applied thereto, the current-voltage characteristic of the said input terminal being such that the current increases continuously for voltage values between zero and the said predetermined threshold value, and is almost zero for voltages higher than this threshold value.
The invention can be used very advantageously in the field of telephony.
Hereinafter, the expression "of any optional length" is to be understood to mean a duration of a great length relative to the said finite duration of the redialling interruption, which is intrinsic to the said dialling circuit comprising the redialling interrupt loop. An interruption of, for example, a duration of the order of 10 times the duration of the finite interruption of the dialling circuit will be considered to be such an interruption of any optional length.
2. Description of the Prior Art
The dialling circuits having a redialling interrupt loop, the interruption being of a finite duration, such as the circuits marketed by "R.T.C.-La Radiotechnique Compelec" under the name PCD 3323, offers the user the possibility to redial automatically a subscriber number already dialled and stored in a memory. For the case in which the subscriber number requires at a given instant a tone signal, for example after the district exchange code or a call abroad, these circuits are provided with an automatic redialling interruption of a finite duration which may be of the order of some seconds. When the delay corresponding to this finite duration has elapsed, the redialling operation is continued until the number to be called is carried through. In the example of the above-mentioned circuit PCD 3323 an interrupt signal appears, when an interrupt command is transmitted by a memory of the circuit at an output terminal, during the finite duration of the interruption, in the form of a d.c. voltage. An input terminal of the circuit is capable of receiving the interrupt signal in order to effectuate the redialling interruption. To realize this redialling interruption in practice, it is sufficient to interconnect the input terminal and the output terminal.
It may happen, in order to prevent, for example the redialling operation from starting again before the tone signal has been obtained, that one wants to have the possibility to give the command to achieve redialling manually by realising a semi-automatic redialling arrangement. For that purpose, it is necessary that on the one hand the interruption can be maintained for a duration of any optional length, and that on the other hand the interruption can be stopped thereafter in order to restart the redialling operation. The present invention has for its object to realize these two functions while making advantageous use of the current-voltage characteristic specific to the input terminal of the circuit PCD 3323.